Power Supply

[Gregory]

I have built a regulated 25 volt power supply. with 10 amp current output
I would like to introduce a current limiting circuit to this power supply so I can regulate the current and voltage as I require them.
I require a circuit digram for this current limiting device to insert it into my power supply.
Could some one assist me with this.
Thank you.

 

[ante]

Gregory,

If you can post the schematic it would be much easier to see what could be done to help you.

Ante :roll:

 

[Gregory]

schematic of power supply

I do not think that the circuit for the current limiting that is veriable is correct. If not could you post the correct schematic for this application .

 

[andrew2022]

u have nothin connected the the +ve output of the bridge rectifier. also it says 5A, not 10

 

[ante]

Gregory,

Have you built the supply exactly like the schematic? Does it work ok so far? I think you will not get away with only one power transistor and 10Amps. If you want an adjustable current limit you can add another LM317 but you also need negative supply for it to work. But there are several diferent ways to do this. It’s not easy to “insert” the extra circuit, you have to rearrange some of the other parts too.

Ante :roll:

 

[checkmate]

Usually, people use multiple power transistors in parallel sharing the same base inputs to support higher current throughputs. For current limiting, they usually use multiple transistors with shunt feedback. But first, you do know of the mistake there with bridge rectifier connections right?

 

[grrr_arrghh]

whats R1 (the pot) doing. The wiper isn't connected to anything, so the resistance will the whole thing will remain constant!?!

 

[zevon8]

Isn't there a problem with the configuration of the pass-transistor too?
It's NPN right?
Why is there a 1 Amp fuse?

I would simply use the reference design by National Semiconductor , or Motorola ( ON I think they call themselves now ) their websites should have PDF's of what you need. They show exactly how to use the LM317 with pass transistors for this type of circuit.

 

[audioguru]

That's a strange circuit, in addition to its rectifier connections and unwired pot sliders:
1) I notice that the current-booster transistor should be a PNP, since an NPN as shown has backwards polarity.
2) The base current of the current-booster transistor will ruin the voltage regulation of the LM317, when it flows through R2.
3) R3 has such a high resistance that the LM317 won't regulate anything.
4) Without a load, if you could somehow keep the current-booster transistor from saturating, then the 30V zener will force the LM317's output to follow the unregulated supply.
5) How do you get 10A (or even only 5A) through the 1A output fuse?

Yeah, National Semi's datasheet shows exactly how to do it properly.
As Ante said, an LM317 adjustable current regulator can be followed by an adjustable LM317 voltage regulator